By Kai Farrimond
A communications satellite for Intelsat launched from Kennedy Space Center’s Launch Complex 39A (LC-39A) on late-Wednesday evening, ascending through the sun-setting sky.
This Falcon 9 was expendable due to the high payload mass and its orbit. This means that there was no landing attempt, no landing legs, and no gridfins.
SpaceX launched Intelsat 35e (or Intelsat 35 Epic) to Geostationary Transfer Orbit on the Falcon 9 Launch Vehicle. This launch will be the last before the eastern range conducts maintenance on ground infrastructure, meaning no launches out of Cape Canaveral/Kennedy Space Center until Early August.
This maintenance will give SpaceX time to return Space Launch Complex 40 back up and running again after a Falcon 9 set to launch Amos-6 for the Israeli Satellite operator, Spacecom, suffered an anomaly while preparing for a Static Fire in September 2016, and destroyed most of the pad with it.
Once SLC-40 is back up and running, Falcon 9 launches carrying commercial payloads will go out from SLC-40 and Falcon Heavy launches, Crew Dragon Missions, and NASA Missions will go out from LC-39A.
Intelsat 35e (IS-35e) is a Geostationary Communications satellite set to cover America, Europe, and Sub-Saharan Africa from the 34.5° West longitude (hence the 35 in the name). The satellite is the fourth in the Epic service and is based on the Boeing 702MP bus. It has a mass of 6.76 Tonnes (6,760 kg) and is expected to be in service for 15 years.
Six days before launch, Falcon rolled out to LC-39A without it’s payload (a customary procedure after September’s anomaly) and went vertical a few hours later. The SpaceX team then went through what is essentially a rehearsal for launch and checking all the vehicle’s systems. The T-0 for the 3.5 second engine firing was originally scheduled for 4pm EST, but was later moved back to 8:30pm.
Finally, at 8:30, the 9 Merlin engines on the base of Falcon ignited for 3.5 seconds and shutdown successfully. Not too long later, a tweet from SpaceX confirmed a good test.
Falcon was then de-tanked of it’s Liquid Oxygen and Rocket Propellant 1 fuels, and rolled back into the Horizontal Integration Facility a quarter of a mile from the launchpad so engineers could attach the Intelsat 35e Payload.
After integration of Intelsat, the vehicle was once again rolled out and raised to the vertical position at around 8:50am EST for it’s first launch attempt on Sunday.
After an abort at T-10 Seconds on the 2nd July due to a GNC (Guidance, Navigation, Control) error, Falcon was ready to launch again 24 hours later.
The 3rd July launch attempt also led to a scrub due to the countdown again entering a hold at T-10 Seconds.
The team took the 4th July to look over vehicle and pad systems and by the 5th July, they were ready for another launch. A T-0 was set for 7:38pm EDT or 11:38pm UTC.
The countdown began early in the day and at T-1 Hour, RP-1 loading began on the vehicle. This is now customary, compared to the usual T-70 Minute start time as SpaceX are trying to get the propellant loading times as close to liftoff as possible. This is now possible thanks to the Block 4 variant of the vehicle. Block 5 is set to debut at the end of the year and introduce many small changes such as the ability for each Falcon 9 first stage to be reused up to 10 times with no refurbishment and many more with slight refurbishment.
At T-37 Minutes, a Go was given to begin the Liquid Oxygen Load and two minutes later, LOX loading began on the vehicle. This is now also customary after debuting on the Iridium-2 mission just one-week earlier.
At around T-4 Minutes, the cradles which support the vehicle upright until the tanks pressurise, slowly opened around the upper stage and a few seconds later, the strongback retracted to it’s 88.5 degree position.
A few minutes later, the Autonomous Flight Termination System, which would destroy the vehicle should a problem arise, was armed and switched to internal power.
At around T-2 Minutes, the Liquid Oxygen loading ended and Falcon completed it’s switch to it’s on board batteries.
At T-60 Seconds, the flight computer took control of all the vehicle’s functions and the vehicle was pressurised for launch.
At T-3 Seconds, the 9 Merlin 1D engines began their ignition sequence and at T-0, and at 7:36pm EST, the hold down clamps released and the strongback rapidly retreated to ~45 Degrees. Falcon was now released and began its ascent.
1 Minute and 18 seconds into the flight, the vehicle experienced Maximum Aerodynamic Pressure (Max-Q) where the highest stresses were applied on the rocket.
2 Minutes and 42 seconds in, the 9 main engines shutoff as planned as the first stage had expended all its propellants.
Then, the first and second stages separated and the second stage ignited its single Merlin 1D Vacuum engine. This engine has a bigger bell than the ones on the first stage, giving it a higher efficiency to work in lower pressure.
The fairing, the composite protecting the satellite during launch, separated at an altitude of 115km at T+3:39.
The first burn of the second stage lasted 5 Minutes and 35 seconds to insert Intelsat and the second stage in a Low-Earth parking orbit. Meanwhile, the first stage descended back through the atmosphere and broke up due to aerodynamic stresses as planned.
At T+8:42, the second stage cutoff and entered an 18 minute coast phase. After this 18 minutes, the second stage re-lit to put Intelsat 35e into an orbit where the highest point is at Geostationary altitude and it’s lowest point is at Low-Earth Orbit altitude. This is known as a Geostationary Transfer Orbit.
This burn lasted 52 seconds after which the MVAC engine shut off and another 5 minute coast until the satellite was deployed.
At T+32:01, the Intelsat 35e communications satellite was deployed, marking a total mission success for SpaceX.
Over the coming weeks, the satellite will use it’s own propulsion systems to raise its perigee and get into a Geostationary Orbit.
SpaceX’s next launch is set to be CRS-12 currently scheduled for early August. SpaceX have said in the past that SLC-40 is expected to be back operational by August so there’s a chance that CRS-12 could be the first launch back from Space Launch Complex 40. If it is, 39A will be shutdown to prepare it for Falcon Heavy. Among numerous other tasks, this will include installing TSM’s (Tail Service Mounts) where the first stage of Falcon 9/Heavy is fuelled.